1. Field of the Invention
The present invention relates to a headlamp for a vehicle and a method of illumination of the headlamp in which a lighting unit for a high beam and a lighting unit for a low beam are tiltably provided as one tilting unit.
2. Description of the Related Art
In the related art, a headlamp for a vehicle comprises a lighting unit for a high beam and a lighting unit for a low beam. The low beam is irradiated by turning on the lighting unit for a low beam whereas the high beam is irradiated by simultaneously turning on both of the lighting units.
In such a headlamp for a vehicle, it is hard to maintain a sufficient distance visibility during the high beam irradiation for the following reasons.
As shown in FIG. 11(a), a light distribution pattern P(L)xe2x80x2 for a low beam, which is formed by the beam irradiation from the lighting unit for a low beam, has a hot zone (high luminous intensity region) HZ(L)xe2x80x2 on a comparatively short distance region in a road placed ahead of a vehicle. Therefore, even if a light distribution pattern P(H1)xe2x80x2 having a hot zone HZ(H1)xe2x80x2 is formed on the long distance region in the road placed ahead of the vehicle by the beam irradiation from the lighting unit for a high beam, the long distance region is seen to be relatively dark due to the hot zone HZ(L)xe2x80x2, making it hard to maintain a sufficient distance visibility.
On the other hand, when the low beam irradiation is switched to the high beam irradiation, as in a headlamp for a vehicle described in JP-A-9-240363, it is possible to enhance the distance visibility at time of the high beam irradiation if only the lighting unit for a low beam is tilted upward and the hot zone of the low beam light distribution pattern is moved to the long distance region in the road placed ahead of the vehicle.
In a headlamp for a vehicle in which a lighting unit for a high beam and alighting unit for a low beam are tiltably provided as one tilting unit, however, there is a problem in that the lighting unit for a low beam cannot be singly tilted upward as in the headlamp for a vehicle described in JP-A-9-240363.
The present invention has been made in consideration of such circumstances and has an object to provide a headlamp for a vehicle in which a lighting unit for a high beam and a lighting unit for a low beam are tiltably provided as one tilting unit, wherein a distance visibility can be enhanced during high beam irradiation.
The invention achieves this object by devising the relationship of a beam irradiation direction between the lighting unit for a high beam and the lighting unit for a low beam.
In that regard, the invention provides a headlamp for a vehicle comprising:
a lighting unit for a high beam and a lighting unit for a low beam tiltably provided as one tilting unit, wherein low beam irradiation is performed by turning on the lighting unit for a low beam and high beam irradiation is performed by simultaneously turning on both of the lighting units,
the lighting unit for a high beam set such that a central luminous intensity position of a light distribution pattern formed by the beam irradiation from the lighting unit for a high beam is lower than a horizontal cutoff line on an opposed lane side in a light distribution pattern for a low beam which is formed by the beam irradiation from the lighting unit for a low beam, and wherein
the tilting unit is operable to be tilted upward at a predetermined angle at the time of the high beam irradiation.
The arrangement of each of xe2x80x9cthe lighting unit for a high beamxe2x80x9d and xe2x80x9cthe lighting unit for a low beamxe2x80x9d is not particularly restricted as they may be provided adjacently in a transverse direction or a vertical direction, for example.
In addition, the specific structures of xe2x80x9cthe lighting unit for a high beamxe2x80x9d and xe2x80x9cthe lighting unit for a low beamxe2x80x9d are not particularly restricted. For example, it is possible to use a so-called parabola type lighting unit having a reflector formed on the basis of a rotation paraboloid, or a so-called projector type lighting unit having a reflector and a projection lens which are formed to take the shape of a deformed elliptical sphere.
The specific structure of a light source for each of xe2x80x9cthe lighting unit for a high beamxe2x80x9d and xe2x80x9cthe lighting unit for a low beamxe2x80x9d is not particularly restricted but it maybe a discharge light emitting portion of a discharge bulb or a filament of an incandescent bulb such as a halogen bulb.
With the structure described above, it is a matter of course that the light distribution pattern formed by the beam irradiation from the lighting unit for a low beam at the time of the high beam irradiation may be maintained to be a light distribution pattern for a low beam. It is also possible to use a light distribution pattern obtained by properly moving the component of the lighting unit for a low beam during beam switching to add a predetermined light distribution pattern to the light distribution pattern for a low beam.
If the xe2x80x9ccentral luminous intensity positionxe2x80x9d of the light distribution pattern for a high beam is set to be lower than the horizontal cutoff line on the opposed lane side in the light distribution pattern for a low beam, a specific position thereof is not particularly restricted but may be properly set depending on the light distribution characteristic of the light distribution pattern for a low beam.
Referring to the xe2x80x9cpredetermined anglexe2x80x9d, a specific value thereof is not particularly restricted but it may be properly set depending on the central luminous intensity position of the light distribution pattern for a high beam; for example, set to approximately 1 to 2 degrees.
With the structure described above, the headlamp for a vehicle according to the present invention is constituted such that a lighting unit for a high beam and a lighting unit for a low beam are tiltably provided as one tilting unit, and low beam irradiation is carried out by turning on the lighting unit for a low beam and high beam irradiation is carried out by simultaneously turning on both of the lighting units. A central luminous intensity position of a light distribution pattern formed by the beam irradiation from the lighting unit for a high beam is set to be lower than a horizontal cutoff line on an opposed lane side in a light distribution pattern for a low beam which is formed by the beam irradiation from the lighting unit for a low beam, and the tilting unit is constituted to be tilted upward at a predetermined angle at time of the high beam irradiation as compared with time of the low beam irradiation. Therefore, the following functions and effects can be obtained.
More specifically, the tilting unit is tilted upward at a predetermined angle during the high beam irradiation as compared with the low beam irradiation so that the light distribution pattern formed by the beam irradiation from the lighting unit for a low beam can be displaced upward at the predetermined angle. Consequently, the hot zone can be moved to a long distance region in a road placed ahead of the vehicle. Thus, it is possible to enhance a distance visibility during the high beam irradiation.
On the other hand, the central luminous intensity position of the light distribution pattern formed by the beam irradiation from the lighting unit for a high beam is set to be lower than the horizontal cutoff line on the opposed lane side in the light distribution pattern for a low beam. Therefore, when the tilting unit is tilted upward at a predetermined angle during the high beam irradiation as compared with the low beam irradiation, the central luminous intensity position of the light distribution pattern can be set to be suitable for enhancing the distance visibility.
According to the invention, therefore, it is possible to enhance the distance visibility during the high beam irradiation in the headlamp for a vehicle in which the lighting unit for a high beam and the lighting unit for a low beam are tiltably provided as one tilting unit.
While the light source for each of xe2x80x9cthe lighting unit for a high beamxe2x80x9d and xe2x80x9cthe lighting unit for a low beamxe2x80x9d is not particularly restricted as described above, it is particularly effective to employ a structure in which the light source of the lighting unit for a high beam is the filament of an incandescent bulb and the light source of the lighting unit for a low beam is the discharge light emitting portion of a discharge bulb.
In explanation, the discharge bulb has a higher color temperature at the time of lighting and a higher luminous flux of a light source than those of the incandescent bulb. Therefore, a light distribution pattern formed by the beam irradiation from the lighting unit for a low beam using the discharge light emitting portion of the discharge bulb as the light source is white and bright, while a light distribution pattern formed by the beam irradiation from the lighting unit for a high beam using the filament of the incandescent bulb as the light source is red and slightly dark. However, with this configuration, the long distance region of the road placed ahead of the vehicle may be seen with more difficulty at the time of the high beam irradiation in which both of the light distribution patterns are synthesized. Consequently, it is more difficult to maintain a sufficient distance visibility. Therefore, it is very effective that the light distribution pattern formed by the beam irradiation from the lighting unit for a low beam is displaced upward at time of the high beam irradiation as in the present invention.
With the structure described above, if the central luminous intensity position of the light distribution pattern formed by the beam irradiation from the lighting unit for a high beam is set to be shifted by a predetermined amount toward the opposed lane side in the forward direction of the lighting unit for a high beam, the following functions and effects can be obtained.
More specifically, the hot zone in the light distribution pattern for a low beam which is formed by the beam irradiation from the lighting unit for a low beam is generally formed in a position shifted toward the self-lane side in the forward direction of the lighting unit for a low beam. Therefore, if the central luminous intensity position of the light distribution pattern formed by the beam irradiation from the lighting unit for a high beam is set to be shifted by a predetermined amount toward the opposed lane side in the forward direction of the lighting unit for a high beam, the hot zone of the synthetic light distribution pattern (that is, the light distribution pattern for a high beam) formed by the beam irradiation from both of the lighting units can be arranged to be transversely expanded with a good balance. Thus, the distance visibility in the high beam irradiation can be enhanced even further. The specific value of the xe2x80x9cpredetermined amountxe2x80x9d is not particularly restricted, but may be properly set depending on the arrangement and size of the hot zone in the light distribution pattern for a low beam and can be set to approximately 0.5 to 2 degrees, for example.